The present invention relates to a syringe for use in a drug infusion system. The syringe is configured to have a relatively tight seal when full, and a relatively loose seal as product is being dispensed. The relatively tight seal helps maintain a gas-tight seal between plunger and barrel during a freeze and thaw cycle to which the syringe and product is exposed. The relatively loose seal permits the plunger to be pushed down the barrel to dispense product with lower force on the plunger, to reduce power consumption of the pump and extend battery life.